Balancing sustainability and performance in transparent anti-soiling coatings

• Systematic tuning of alkylsilane chain length controls roughness and anti-soiling behavior. • Minimal fluorinated content enables sustainable, transparent coatings without loss of function. • Only 5% FAS is sufficient to achieve durable, high-performance anti-soiling coatings. Transparent, anti-soiling coatings are essential for mitigating dust-related efficiency losses in solar energy, but reliance on environmentally concerning fluoroalkylsilanes (FAS) remains a challenge. This study investigates a strategy to minimize FAS content by systematically blending alkylsilanes of varying chain lengths (C16, C8, C4), via a sol–gel process. We explore the fundamental interplay between surface energy and roughness across 14 formulations to establish design principles for sustainable coatings, using XPS, AFM, and SE measurements. Our key finding is a critical transition in the dominant anti-soiling mechanism at a surface energy of ∼20 mN/m. Above this threshold, performance is highly sensitive to roughness. Below it, low surface energy dominates, ensuring excellent performance even with higher roughness. This principle enables us to demonstrate that a minimal FAS content of just 5% is sufficient to cross this critical threshold and achieve durability and high performance, providing a pathway to drastically reduce fluorinated content without compromising functionality.